id Tech 1 games: Customizable ammo capacity

[KScl]

This is the AP counterpart to Daivuk/apdoom#18. Now that that commit has been merged in, this one is ready for review as well, as the client is now capable of handling the items added in this commit.

What is this fixing or adding?

Adds the following options to every id Tech 1 game:

• split_backpack / split_bag_of_holding
  • In the Doom games, splits the Backpack into four separate capacity upgrade items, one for each ammo type.
  • In Heretic, splits the Bag of Holding into six separate capacity upgrade items, one for each ammo type.
• backpack_count / bag_of_holding_count
  • Sets the amount of Backpacks or Bags of Holding that get added to the item pool, from 0 to 10.
  • These pickups now stack, so having multiple of them results in greater ammo capacity, up to a maximum of 999.
  • With the above option to split the Backpack or Bag of Holding, there will be this many copies of each capacity upgrade item.
• max_ammo_(type)
  • Sets the maximum ammo you're allowed to carry for each ammo type at the start of the game.
  • Range varies, from the default starting value for that ammo type to a maximum of 999.
• added_ammo_(type)
  • Sets the amount of ammo capacity gained from each Backpack, Bag of Holding, or capacity upgrade item.
  • Range varies, from 1/10th of the default ammo capacity value, to a maximum of 999.

Backpacks, Bags of Holding, and the new capacity upgrade items are now considered Useful instead of Progression. This has only changed logic for two extremely late game levels in Heretic (E5M8 and E5M9), which have had their logical Bag of Holding requirement removed. This was done because otherwise progression fill was really unhappy with the number of added Progression-marked items that don't actually give progression in any meaningful way.

How was this tested?

Many weeks of generation and playtesting, both locally and in sync games with friends.

[Daivuk]

The changes in items.py and rules.py, did you made them directly here? Or did you use the tool to generate the files?
If you didn't use the tool, then next time we regenerate stuff it will override your changes.

[KScl]

They're all generated using ap_gen_tool; I make it a point not to modify the five python scripts it auto-generates directly, for precisely that reason.

[Daivuk]

All good from me